阅读说明：本技术 一种混合plc/vlc系统联合用户配对和子载波分配方案 (Combined user pairing and subcarrier allocation scheme for hybrid PLC/VLC system ) 是由 刘焕淋 朱平鑫 陈勇 浦欣 陈金林 于 2020-06-05 设计创作，主要内容包括：本发明涉及一种混合PLC/VLC系统联合用户配对和子载波分配方案,属于电力线通信、光通信技术领域。在用户配对阶段,判断用户数是否可以被4整除,若可以,将用户按照信道增益降序分成四组,第一组和第三组以及第二组和第四组分别按照最优用户配对方案配对；否则,将按信道增益排列的第一个用户和最后一个用户配对,剩余用户按照能够被4整除进行最优用户配对。在子载波分配阶段,每一次迭代依次执行轮盘赌操作、基于交叉临界值的交叉操作和自适应变异操作,直到满足收敛条件,此时输出所有配对用户对的子载波分配方案。本发明所述方法在保证混合PLC/VLC系统和速率的同时,能够降低计算复杂度,并且还能兼顾混合PLC/VLC系统公平性和用户满意度。(The invention relates to a combined user pairing and subcarrier allocation scheme of a hybrid PLC/VLC system, and belongs to the technical field of power line communication and optical communication. In the user pairing stage, judging whether the number of users can be divided by 4, if so, dividing the users into four groups according to the descending order of channel gain, and pairing the first group and the third group and the second group and the fourth group according to the optimal user pairing scheme respectively; otherwise, the first user and the last user which are arranged according to the channel gain are paired, and the rest users are subjected to optimal user pairing according to the integer division of 4. In the sub-carrier allocation stage, the roulette operation, the crossing operation based on the crossing critical value and the adaptive variation operation are sequentially executed in each iteration until a convergence condition is met, and then the sub-carrier allocation schemes of all the paired user pairs are output. The method of the invention can reduce the calculation complexity while ensuring the mixing PLC/VLC system and the speed, and can also give consideration to the fairness and the user satisfaction degree of the mixing PLC/VLC system.)

1. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme, characterized in that: the scheme comprises the following steps:

s1: according to respective channel models of the PLC and the VLC, the relay LED is considered to amplify and forward the received PLC signal, and a channel model of the hybrid PLC/VLC system is deduced;

s2: calculating the average channel gain of each user for all users accessing the hybrid PLC/VLC system;

s3: for all users accessing the hybrid PLC/VLC system, carrying out user pairing by using an optimal user pairing scheme;

s4: for the paired user pairs, carrying out subcarrier allocation by using an improved genetic algorithm;

s5: and outputting the user pairing and subcarrier allocation scheme of the hybrid PLC/VLC system.

2. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S1 is as follows:

s101: an input signal is influenced by PLC channel gain and noise through a PLC channel, an LED serves as a relay of a hybrid PLC/VLC system, and an amplification forwarding mode is adopted to amplify an output signal in the PLC channel by beta times and then forward the amplified output signal to the VLC channel;

s102: the signal serves as an input signal for the VLC channel, affected by the gain and noise of the VLC channel, and transmitted to each user.

3. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S2 is as follows:

s201: for the presence of N_PSub-carrier, mixed PLC/VLC system for U users, may have N_P× U channel gains, user U has one channel gain per subcarrier, i.e.

S202: according to the formulaCalculate the average channel gain h for user u_u|。

4. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S3 is as follows:

s301: in descending order according to the average channel gain of all users, with the user channel gain being in the frontThe users of (1) are in a first group, and the user channel gains are ranked inTo

s302: matching the users in the first group with the users in the third group by adopting an optimal user matching scheme; similarly, the users in the second group and the users in the fourth group are paired.

5. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S4 is as follows:

s401: the fitness function is the basis for selecting chromosomes by a genetic algorithm, and in order to balance the fairness of the speed among users, the fitness function based on the fairness is provided;

s402: the genetic algorithm is easy to fall into a local optimal solution, a large number of iterations are usually required to be set, in order to improve the convergence performance and the convergence speed of the algorithm, the cross operation and the mutation operation of the genetic algorithm are improved, and a cross mode and a self-adaptive mutation operation based on a critical value are adopted;

s403: judging whether the evolution algebra is larger than the set maximum value or whether the optimal individual fitness value of the continuous 15 generations is unchanged and is not satisfied, returning to S401 and S402 to continue iterative computation; if so, the iteration ends.

Technical Field

The invention belongs to the technical field of optical communication, and relates to a combined user pairing and subcarrier allocation scheme of a hybrid PLC/VLC system.

Background

With the rapid increase of the number of mobile communication users, Radio Frequency (RF) communication occupies a more crowded Radio wave frequency band, and Visible Light Communication (VLC) based on light emitting diodes becomes a high-speed wireless access scheme with great potential due to the advantages of low power consumption, no electromagnetic interference, large available bandwidth, no authentication, and the like. However, visible light cannot be directly used as an information source, and information islanding can be avoided by accessing a backbone network, and in all backbone network candidates, the power line communication can utilize the existing infrastructure of each Light Emitting Diode (LED) without additional wiring. Therefore, it is proposed to provide data to VLC transmitters using Power Line Communication (PLC), and a hybrid PLC/VLC system architecture for indoor downlink transmission is proposed. However, the conventional multiple access method cannot optimally utilize resources. Therefore, Non-Orthogonal Multiple Access (NOMA) has attracted considerable attention, which provides higher spectral efficiency by allowing Multiple users to share the same time and frequency resources. The existing research shows that: the introduction of the NOMA technology into the VLC network can improve the multi-user visible light communication system and rate, but does not limit the number of users in one subcarrier, and when a plurality of users share one subcarrier, higher computational complexity and decoding delay are caused. Therefore, 2 users form one NOMA group to use one subcarrier, and different NOMA groups use different subcarriers, and it is the focus of research to design a reasonable joint user pairing and subcarrier allocation scheme for users.

Disclosure of Invention

In view of this, an object of the present invention is to provide a hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme, which is used for performing user pairing and subcarrier allocation for multiple users in a hybrid PLC/VLC system based on NOAM technology, and can reduce computational complexity while ensuring the hybrid PLC/VLC system and rate, and also can consider fairness and user satisfaction of the hybrid PLC/VLC system.

In order to achieve the purpose, the invention provides the following technical scheme:

a hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme, characterized in that: the scheme comprises the following steps:

s1: according to respective channel models of the PLC and the VLC, the relay LED is considered to amplify and forward the received PLC signal, and a channel model of the hybrid PLC/VLC system is deduced;

s2: calculating the average channel gain of each user for all users accessing the hybrid PLC/VLC system;

s3: for all users accessing the hybrid PLC/VLC system, carrying out user pairing by using an optimal user pairing scheme;

s4: for the paired user pairs, carrying out subcarrier allocation by using an improved genetic algorithm;

s5: and outputting the user pairing and subcarrier allocation scheme of the hybrid PLC/VLC system.

2. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S1 is as follows:

s101: an input signal is influenced by PLC channel gain and noise through a PLC channel, an LED serves as a relay of a hybrid PLC/VLC system, and an amplification forwarding mode is adopted to amplify an output signal in the PLC channel by beta times and then forward the amplified output signal to the VLC channel;

s102: the signal serves as an input signal for the VLC channel, affected by the gain and noise of the VLC channel, and transmitted to each user.

3. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S2 is as follows:

s201: for the presence of N_PSub-carrier, mixed PLC/VLC system for U users, may have N_P× U channel gains, user U has one channel gain per subcarrier, i.e.

S202: according to the formulaCalculate the average channel gain h for user u_u|。

4. A hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S3 is as follows:

s301: in descending order according to the average channel gain of all users, with the user channel gain being in the frontThe users of (1) are in a first group, and the user channel gains are ranked inTo

The users of (1) are in a second group, and the user channel gains are ranked in

To

The users of (2) are in a third group, and the user channel gains are ranked inThe users to U are in the fourth group;

s302: matching the users in the first group with the users in the third group by adopting an optimal user matching scheme; similarly, the users in the second group and the users in the fourth group are paired;

5. a hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme as in claim 1, wherein: the specific method of S4 is as follows:

s401: the fitness function is the basis for selecting chromosomes by a genetic algorithm, and in order to balance the fairness of the speed among users, the fitness function based on the fairness is provided;

s402: the genetic algorithm is easy to fall into a local optimal solution, a large number of iterations are usually required to be set, in order to improve the convergence performance and the convergence speed of the algorithm, the cross operation and the mutation operation of the genetic algorithm are improved, and a cross mode and a self-adaptive mutation operation based on a critical value are adopted;

s403: judging whether the evolution algebra is larger than the set maximum value or whether the optimal individual fitness value of the continuous 15 generations is unchanged and is not satisfied, returning to S401 and S402 to continue iterative computation; if so, the iteration ends.

The invention has the beneficial effects that: the invention provides a hybrid PLC/VLC system joint user pairing and subcarrier allocation scheme, and the NOMA technology is used in the hybrid PLC/VLC system, so that the spectrum efficiency can be improved, and the hybrid PLC/VLC system and the rate are improved; the NOMA technique allows multiple users to share one subcarrier, which results in higher computational complexity and decoding delay. Therefore, 2 users are paired to form one NOMA group to use one subcarrier, and different NOMA groups use different subcarriers, so that the computation complexity can be reduced while the hybrid PLC/VLC system and speed are ensured, and the fairness of the cascaded PLC-VLC system and the satisfaction degree of the users can be considered.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.

Drawings

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of a hybrid PLC/VLC system model;

fig. 2 is a flowchart of a hybrid PLC/VLC system joint user pairing and subcarrier allocation based on NOMA technology.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.

Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in any way limiting the scope of the invention; to better illustrate the embodiments of the present invention, some components of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

FIG. 1 shows a block diagram of a hybrid PLC/VLC system model.

FIG. 1 shows a block diagram consisting of N_LEach LED lamp is N at the same time_UIn the hybrid PLC/VLC system served by each user, a power line serves as a backbone network to provide data for a plurality of LED lamps with VLC and coordinate the cooperation of the LED lamps, and the LED lamps also operate as full-duplex relays to process received PLC signals and forward the PLC signals to indoor users through VLC. Each luminaire transmits only a subset of the data symbols from the received PLC signal. VLC signals from multiple LED emitters are superimposed at a photodiode detector of a user, where a receiver may be used to decode the information. PLC link includes N_PAnd each independent subcarrier carries information. In VLC link, N that k LED luminaire will receive_kThe PLC data symbols are re-modulated onto VLC subcarriers. The subcarrier subsets on different luminaires are disjoint and satisfyIn each LED lamp, the inventionConsider a subcarrier pairing method to adaptively match input and output subcarriers to fully exploit the frequency diversity of PLC and VLC channels.

Power line channel transfer function formula:

each path i has a weighting factor g_iWhich represents the reflection and transmission factor of this path, -1. ltoreq.g_iLess than or equal to 1. The more refraction and reflection in a path g_iThe smaller. a is₀，a₁Are all constant. Tau is_i＝l_i/v_p，τ_iIndicates the delay time of the ith path,/_iIndicates the length of the ith path, v_pIndicating the phase velocity.

X_p(l) Representing the frequency domain transmission symbol on subcarrier l in PLC, the invention uses NOMA technique, LED uses superposition coding to multiplex N on each subcarrier_UThe signal of the individual user.The frequency domain signal representing the signal of user u on subcarrier l of the PLC received by the kth LED luminaire.

Wherein

And

respectively representing the channel gain and noise of the signal of user u on subcarrier i at fixture k in the PLC,representing having zero mean and variance

The noise of the gaussian noise of (a),

the VLC channel gain between the receiver and the light source may be expressed as:

wherein A is_PDIs the surface area of the PD,is the gain of the optical filter and is,is the gain of the optical lens, n is the refractive index,

is the field angle of the PD.

Representing the frequency domain transmission symbol on subcarrier n in the kth LED fixture,

is the amplification factor of the signal to be amplified,

representing the frequency domain signal of user u on subcarrier n on the kth LED fixture.

Wherein

Andrepresenting the channel gain and noise of user u on subcarrier n in the kth LED fixture,representing having zero mean and variance

The noise of the gaussian noise of (a),

thus, in a hybrid PLC/VLC system, the channel gain on the paired subcarriers (l, n) is:and noise on the paired subcarriers isRepresenting having zero mean and varianceThe noise of the gaussian noise of (a),the paired sub-carrier (l, n) is next denoted by sub-carrier l.

In order to balance between system performance and computational complexity, the present invention proposes a hybrid scheme of NOMA and OMA, i.e. 2 users are paired into a group, and one NOMA group is formed to use one subcarrier, while different NOMA groups use different subcarriers. Considering that the channel conditions of users are different in an indoor environment, in order to guarantee the rate of each user and improve the fairness among users, the invention provides a Joint User Pairing and Subcarrier Allocation (JUPSA) scheme based on the fairness. Firstly, all indoor users are paired with the aim of maximizing the system and the rate, the paired users are one NOMA group, and then all the paired NOMA groups are subjected to subcarrier allocation.

If the number U of users is odd, it is inevitable that one user does not pair, and occupies one subcarrier alone. If the number of users U is even, all users will be paired into a NOMA group. For N_PA system of sub-carriers, U users, will have N_P× U channel gains, for example, user 1 would have one channel gain in each subcarrier, i.e.

Define the average channel gain of user u as h_u|。

The optimal user pairing scheme indicates that for U users in the system, without loss of generality, it is assumed that the channel gain of the users satisfies | h₁|＜|h₂|＜…＜|h_UAnd when the user m is paired with the user U-m +1, for example, the user 1 is paired with the user U, the user 2 is paired with the user U-1, and the sum rate of the system is the maximum. However, in the above pairing rule, it may occur that two adjacent users are paired together, i.e. users

And the userAre paired together. In view of the problem, the present invention proposes to divide the users sorted in ascending order of average channel gain into four groups, and the users of the first group are paired with the users of the third group, the users of the second group are paired with the users of the fourth group, and the pairing scheme of each two groups is consistent with the optimal user pairing scheme, thereby avoiding the adjacent users from being paired together, and enabling the system and the rate to be maximized.

There are many possible schemes for the matched users to be allocated to different subcarriers, but the system performance is different in all the schemes, and in order to find the best subcarrier allocation scheme, the invention adopts an intelligent optimization algorithm, namely a genetic algorithm, but the genetic algorithm is easy to fall into local optimization, and usually a large number of iterations are required to be set. In order to improve the convergence performance and the convergence speed of the algorithm, an improved genetic algorithm is provided for subcarrier allocation.

Fitness function based on fairness

The fitness function is the basis for genetic algorithm to select chromosomes, and the design of the fitness function is very important. The fitness function f (c) of the designed individual is as follows:

in the formula (7), R_iThe rate of user i. The maximization of the system logarithm and the speed can realize the balance of speed fairness among users while improving the system and the speed, namely, the fairness of the system is improved.

② chromosome structure

Each locus in the chromosome represents the subcarrier number, the value (i, j) of the locus n_n(i,j∈U,n∈N_P) Representing subscriber pairs served by subcarrier n, a set of subcarrier allocation results together forming a chromosome

For example chromosome c₁＝[(1,6)₁,(2,5)₂,(3,8)₃,(4,7)₄,(1,6)₅]Represents: the hybrid PLC/VLC system has 5 subcarriers in total, and serves 4 user pairs and 8 users; the service subcarrier sets of the paired users (1,6) are {1,5}, the service subcarrier sets of the paired users (2,5) are {2}, the service subcarrier sets of the paired users (3,8) are {3}, and the service subcarrier sets of the paired users (4,7) are {4 }.

(iii) genetic manipulation

The improved genetic algorithm operation provided by the invention comprises selection operation, crossover operation and mutation operation. The selection operation adopts roulette selection, the roulette selection selects an individual according to the fitness function value of the individual, the individual with a high fitness function value is selected, the survival probability is higher, and the probability that the individual is selected in the selection operation is as follows:

u in formula (8) is the number of individuals in a population,is the sum of fitness function values of all individuals in the population.

In the traditional genetic algorithm, a two-point crossing mode is mostly adopted, namely two crossing points are randomly generated, and genes between the two crossing points are interchanged. However, as the population is continuously evolved, the difference between individuals in the population is gradually reduced, so that the similarity degree between the individuals is gradually improved, and the crossing operation of two parent individuals with high similarity degree damages a good gene pattern and also leads to more iteration times. The formula for the crossover threshold is:

in the formula (9), r represents a cross threshold, a represents the evolution number of the population at that time, and G represents the total evolution number specified by the population. From the above formula, r is one

The number between them is not fixed and is continuously increased along with the increase of the current evolution algebra. The similarity of two individuals is defined as:

in the formula (10), s represents the similarity of two individuals, c represents the length of the longest common substring of the two individuals, and n represents the length of the chromosome code of the individual in the population. And if the similarity s of the two parent individuals needing to be crossed is smaller than the current crossing critical value r, allowing the two parent individuals to be crossed. If the similarity s of the two parents needing to be crossed is greater than or equal to the current cross critical value r, the two parents are not allowed to be crossed so as to avoid destroying the good gene patterns of the two parents.

Operation of variation

The method adopts self-adaptive mutation operation, and self-adaptively adjusts the mutation probability according to the maximum fitness value and the average fitness value of chromosomes in the population. The adaptive mutation probability formula is:

in the formula (11), P_mmaxTo preset the maximum variation probability, f_avgIs the mean fitness value of chromosomes in the population, f_maxIs the maximum fitness value of the chromosomes in the population, and f is the fitness value of the chromosomes to be mutated.

The implementation of the method will be described in detail below with reference to fig. 2:

inputting: indoor system parameters (size of indoor environment, number of indoor users, number of subcarriers, device parameters of LED array, receiver location, parameters of receiver, etc.). The algorithm executes the required parameters (amplification factors, filter gains, etc.).

And (3) outputting: and the user pairing scheme and the subcarrier allocation scheme of the paired users in the cascaded PLC-VLC system.

Step 1: judging whether the total number of users in the cascaded PLC-VLC system can be divided by 4, if so, turning to the step 2; otherwise, the first user and the last user which are arranged according to the channel gain are independently paired, the remaining U-2 users are divided into four groups from large to small according to the channel gain, the first group and the third group are paired according to the optimal user pairing scheme, the second group and the fourth group are paired according to the optimal user pairing scheme, and the step 3 is switched.

Step 2: dividing the users into four groups from large to small according to the channel gain, pairing the first group and the third group according to the optimal user pairing scheme, pairing the second group and the fourth group according to the optimal user pairing scheme, and turning to the step 3.

And step 3: initializing the population, making the evolution algebra a of the genetic algorithm equal to 0, and turning to step 4.

And 4, step 4: and (5) calculating the fitness value of each individual in the population according to the formula (7).

And 5: judging whether the evolution algebra a is larger than a preset maximum evolution algebra a_maxOr whether the optimal individual fitness value in the continuous 15-generation population is unchanged, if so, outputting a user pairing scheme and subcarrier allocation schemes of all paired users, and ending the algorithm; otherwise, go to step 6.

Step 6: a roulette selection is performed, step 7.

And 7: crossing the chromosome based on the crossing threshold according to the formulas (9) and (10), and turning to step 8.

And 8: and (5) carrying out self-adaptive mutation on the chromosome according to the formula (11), and turning to the step 9.

And step 9: and (4) generating a new population, wherein the evolution generation number a is a +1, and turning to the step 4.

Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.